In the normal course of packinghouse operations, a large quantity and variety of meat must be "boned out". Thus, in order to produce a boneless ham, a butcher must first remove the bone from the hind leg of the hog. This is done with a simple knife, and when skillfully performed, only a relatively small amount of meat remains on the bone. In other cases, particularly when removing the back bones and neck bones of cattle and hogs, the bones contain substantial amounts of meat, since it is not feasible to follow the irregular surface of each vertebrae with a simple knife. These bones are often trimmed further using a motorized rotary knife working on one bone at a time, which recovers additional valuable meat in the form of small trimmings, but the cost of labor makes this technique applicable only to bones containing relatively large qualities of meat, and more important, even after trimming in this manner, the trimmed bones still contain substantial amounts of valuable meat.
Thus, the meat packer seeks to leave as little meat as possible on the bones, since the latter are worth very little, whereas the meat, if, in the form of small trimmings, is many times more valuable. An integrated meat packer is able to utilize meat trimmings in the preparation of many varieties of luncheon meats, bologna and wieners, since, for this purpose, the various ingredients must be ground or comminuted in any case.
An important consideration is that the meat recovered from the bones be in a raw state, rather than cooked. This is due to the fact that cooked meat possesses little or no "binding capacity", while raw meat possesses high "binding capacity". Binding capacity refers to the ability of the meat to form a stable mixture with added fat, water and salt, which is not broken down during the normal processing (cooking) operations in the manufacture of wieners, bologna, etc. Thus, the raw meat is considerably more valuable to the packer for this purpose than is cooked meat.
Some of the existing techniques for removing residual meat from bones are as follows:
(1) Enzymatic attack.
The meat-containing bones are subjected to the action of proteolytic enzymes which loosen the meat-to-bone bond at elevated temperatures. See Canadian Pat. No. 646,042 and U.S. Pat. No. 3,293,687. As discussed above, this method produces the removed meat in a cooked form.
(2) Puffing gun.
The bones are subjected to rather high steam pressures for a short time. Upon suddenly releasing this pressure, the meat is separated from the bone by the sudden liberation of heat. Again, the removed meat is in a cooked or partially cooked condition. See U.S. Pat. No. 3,129,455.
(3) Shot blasting.
In U.S. Pat. No. 3,089,775, bones are shot blasted with particles of ice or dry ice to remove the meat. The ice is then melted and drained off. (4) Mechanical methods. In this category there are a variety of approaches in which the bones are subjected to some form of mechanical contact to remove the residual meat in raw condition.
(a) In Canadian Pat. No. 711,844, bones are conveyed past rotary brushes.
(b) In Canadian Pat. No. 743,694, the bones are flailed with rotating chains.
(c) In Canadian Pat. No. 573,876, bones are conveyed repeatedly past a second conveyor containing meat-removing knives.
(d) In Canadian Pat. No. 698,939 and U.S. Pat. No. 3,112,203, water is added to crushed or comminuted bones, and the mass is violently agitated to free the meat from the bone particles and form a slurry containing both meat and bone. The mixture is centrifuged to remove the bone and then further centrifuged to dewater the meat tissue. The water fraction contains dissolved protein, and may be spray dried in order to recover this valuable protein.
(e) In U.S. Pat. No. 3,028,243, the process is similar in principle to (d) above, but the centrifugally separated meat product retains the added water, obviating the need for spray-drying.
(f) In U.S. Pat. No. 2,895,162, the residual meat is stripped from bones by passing through a hammermill like apparatus with flat knife-type hammers and slotted discharge plate.
(g) In U.S. Pat. No. 3,142,860, the residual meat is shredded from bones during passage through a platen having yieldable projections.
(h) In U.S. Pat. Nos. 3,266,542, 3,266,543 and 3,256,555, the residual meat is separated from bone particles during passage through a plurality of closely spaced cutting elements, or alternatively through opposed sets of cutting, scrapping and tearing elements.
(5) Tumbling method.
In U.S. Pat. No. 3,594,190, the bones containing raw meat are tumbled in a rotating drum in the presence of water or brine solution to abrade the meat from the bones by the combined action of the solution and of the bones falling and rubbing repeatedly upon themselves to form a meat slurry which is then drained off from the cleaned bones for use directly in sausage or the like manufacture where it inputs good binding power and adds food value. This method is illustrated in flow diagram form in FIG. 1.